Do you specifically not want to use mobile internet when abroad?

Ensure then that roaming has been disabled on your device. Go to Apps > Settings > More > Mobile networks > Data roaming to disable roaming.

Are you experiencing problems calling or being called when abroad?

If you are experiencing problems making or receiving calls, there may be a problem with the network coverage. This is probably due to your location, for example a garage or concrete building. Test to see if a change of location helps.

If this fails, check the network coverage in your area, or see if changing networks helps. Read the instructions below for this.